Accretion patterns of Belize barrier and atoll reefs: an archive of environmental change during the Holocene
Final Report Abstract
Tropical coral reefs, as prominent marine diversity hotspots, are in decline, and long-term studies conducted by geoscientists help to improve the understanding of the effects of global warming, sea-level rise, ocean acidification, deterioration of water quality, and diseases of reef-building organisms. Twenty-two existing drill cores from Belize barrier and atoll reefs, the largest reef system in the Atlantic Ocean were investigated with regard to changes in coral abundances and reef growth together with ReefTech Inc., Miami, Florida, University of Ottawa, Canada, GEOMAR Kiel, GSI Darmstadt, and the Institute of Nuclear Physics of Goethe University. The core material comprises the past ca. 9,000 years, i.e., the major part of the Holocene, the youngest section of earth history. Following the last ice age, the Holocene was characterized by rapid temperature and sea-level rises that subsequently have slowed down. In this general situation, tropical coral reefs developed over the past ca. 10,000 years in that they colonized former exposed areas on oceanic shoals and on continental shelves in the form of atolls, barrier reefs, and fringing reefs. The drill cores were dated in that the age of 76 new coral samples was measured using the uranium-thorium method. Distances between dated corals were used to estimate coral growth (or accretion) rates. It was shown that accretion rates have decreased during the Holocene and the mean rate of 3.36 meters per thousand years (or 3.36 mm per year) is located at the lower end of reef growth compilations from other regions and at the lower limit of prognosed rates of sea-level rise until the end of the 21st century. The latter is especially crucial for the 80 million inhabitants of tropical island nations, one percent of the world's population, who will likely lose their homelands during the next decades. The paleontological investigations of the cores from Belize reefs have shown that branched Acropora palmata corals and the massive star corals (Orbicella spp.) have been the most common corals. The abundance of competitive, fast-growing acroporids and that of fire corals (Millepora spp.) was constant over multi-millennial timescales. But some Acropora corals exhibit declines in abundance and three centennial-scale gaps in the fossil record. These observations suggest that the modern decline in acroporids was apparently not unprecedented. Stress-tolerant corals such as the star coral (Orbicella spp.), the starlet coral (Siderastrea spp.), and brain corals (Pseudodiploria spp.) were abundant at the beginning of Holocene successions, but their abundances have decreased later on during the Holocene. The abundance of weedy corals such as the finger and hill corals (Porites spp.) and the salad coral (Agaricia spp.) on the other hand has increased during the Holocene underlining the increasing importance of fecundity for the coral community.
Publications
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A quantitative approach to Holocene tropical reef accretion: the influence of sea level, subsidence, and climate.- 14th International Coral Reef Symposium, Bremen.
Gischler, E.
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The Belize barrier and atoll reefs revisited: new data on Holocene reef accretion and the impact of sea level, subsidence, and climate. 15th International Coral Reef Symposium, Bremen. Talk
Gischler, E., Hudson, J.,H., Pisera, A., Stocchi & P. Eisenhauer, A.
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9000 years of change in coral community structure and accretion in Belize reefs, western Atlantic. Scientific Reports, 13(1).
Gischler, Eberhard; Hudson, J. Harold; Eisenhauer, Anton; Parang, Soran & Deveaux, Michael
